1. Field
This disclosure relates to acousto-optic devices having multi-layer nanostructures, and to optical scanners, optical modulators, and display apparatuses using the acousto-optic devices, and more particularly, to an acousto-optic device capable of increasing a range of a diffraction angle of output light or adjusting a diffraction angle characteristic of the output light by using an acousto-optic medium having a multi-layer nanostructure formed of metal and dielectric materials, and to an optical scanner, an optical modulator, and a display apparatus using the acousto-optic device.
2. Description of the Related Art
The acousto-optic effect is an effect in which a refractive index of light is periodically varied in a medium by a series of compressions and rarefactions in the medium produced by sonic waves such as ultrasonic waves propagating in the medium. The series of compressions and rarefactions produces a phase grating in the medium, which diffracts light incident on the medium. In general, a medium exhibiting the acousto-optic effect is called an acousto-optic medium. An intensity and a diffraction angle of diffracted light produced by the phase grating in the medium depend on an intensity of the sonic waves and a frequency of the sonic waves, respectively. Thus, an acousto-optic device having a sonic wave generator such as an ultrasonic wave generator on a surface of the medium having the aforementioned characteristic may be used in an optical modulator for modulating the amplitude of incident light, or in an optical scanner for deflecting incident light.
However, acousto-optic devices that use raw mediums existing in the natural world have a limited range of a diffraction angle of output light due to a limited optical anisotropy and a limited acousto-optic coefficient of the mediums. That is, in an acousto-optic according to the related art, a range of a diffraction angle of output light is too narrow. Thus, when an acousto-optic device according to the related art is used in various optical application fields, including an optical scanner, an optical modulator, a display or the like, a separate optical system is required to compensate for the narrow range of the diffraction angle. This separate optical system increases a size of the system and/or may reduce a resolution of the system. Accordingly, research into various structures of the acousto-optic medium and an increase in a range of a diffraction angle of the acousto-optic device have been conducted.